This invention pertains to an antenna for electromagnetic energy, and more particularly to such an antenna which is bidirectionally focused.
I have discovered that the phenomenon of standing waves in an electromagnetic transmission medium can be used advantageously in investigating various internal conditions in different substances. For example, this phenomenon can be used to monitor physiological conditions within different parts of a person's body, and can also be used, as a further illustration, in an application such as flaw detection in metals. More specifically, by directing electromagnetic radiation of a known wavelength toward what might be thought of as an interrogation zone inside a substance, and through locating this zone at, for example, a distance of substantially one-quarter of the wavelength of the radiation from the central radiating element in an antenna, measurements may be made at another point along the transmission axis of the antenna which will provide a direct indication of electrical characteristics, such as impedance, within the interrogated zone.
A general object of the present invention is to provide a unique antenna for bidirectionally radiating energy so as to take full advantage of this standing-wave measurement possibility.
More specifically, an object of the invention is to provide such an antenna which operates in a bidirectional manner with respect to a central element in the antenna.
Still another object of the invention is to provide such an antenna which is constructed in a special manner so as to focus radiation bidirectionally at a pair of spaced-apart focal points that are disposed symmetrically with respect to the antenna, and are spaced by a distance substantially equaling one-half the wavelength of the radiation intended for the antenna.
A preferred embodiment of the proposed antenna features a central, generally ring-like radiation-effective expanse, which has a nominal circumference equaling the wavelength of the radiation planned for the antenna. Fitted symmetrically with respect to this expanse is a specially shaped lens which produces a pair of symmetrically spaced focal points relative to the expanse--such points being separated by the half-wavelength distance mentioned above.
The expanse just mentioned, which is also referred to as the driven expanse in the antenna, is driven at a pair of diametrically opposed points, with signals fed to these points being substantially exactly 180.degree. out-of-phase. As a consequence of this arrangement, radiation actually occurs from a pair of points on the expanse disposed in quadrature with respect to the driving connection just mentioned. The fact radiation occurs from points is a feature which greatly enhances the overall resolution obtainable at the focal points of the antenna. Radiation emanating from the two radiation points is directed in opposite directions along what might be thought of as the transmission axis of the antenna toward the antenna's focal points. The fact that two points of radiation are employed, which points are spaced apart, greatly facilitates focusing of radiated energy at the focal points.
When the antenna is used, it is contemplated that it will be adjusted so as to place one of its two focal points adjacent a selected interrogation zone. The size of the interrogation zone is determined, essentially, through the size of a conductive receiver, which is used along with the antenna, and is located adjacent the other focal point. A form of receiver which is shown herein, and which has been found to be extremely effective, is a short section of conductive tubing, whose cross-sectional area and whose axial length define the volume of the interrogation zone. Preferably, a relatively small receiving tube is used, and this is placed somewhat toward the antenna from the adjacent focal point. The receiver is not placed exactly at the location of the focal point inasmuch as, in order to be effective there, it would have to have infinitesimally small dimensions.
As will become apparent, in order to obtain maximum resolution, maximum accuracy, and maximum versatility in the antenna, there are a number of important dimensional and shape characteristics which will be mentioned below. Further, it should be noted that while the antenna is specifically described herein in connection with an operation wherein it functions primarily as a transmitting antenna, the same construction could be used as primarily a receiving antenna which has highly focused directional receiving capabilities.
Through achieving precise high-resolution focusing in a bidirectional manner, the antenna of the invention greatly facilitates the unique kind of internal investigation technique mentioned above. With the antenna in use, and with one of its focal points directed toward a zone for interrogation within a body, it is a simple matter to monitor electrical conditions of energy received by the receiving tube, and to interpret these conditions as an indication of electrical characteristics within the monitored zone. These characteristics, in turn, are interpretable to indicate various physical conditions existent in the interrogated zone.
These and other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.